Legendary Resistance (3/Day). If the Vestige of the Dragon fails a saving throw, it can choose to succeed instead.

Incorporeal Movement. The Vestige of the Dragon can move through other creatures and objects as if they were difficult terrain. It takes 5 (1d10) force damage if it ends its turn inside an object.

Innate Spellcasting. The Vestige of the Dragon's spellcasting ability is Charisma (spell save DC 23). It can innately cast the following spells, requiring no material components:

1/day each: bane, counterspell, danse macabre, dissonant whispers, illusory dragon, shadow of moil, spirit guardians, summon greater demon, temple of the gods

Multiattack. The Vestige of the Dragon can use its Horrifying Visage. It then makes three attacks: one with its bite and two with its claws.

Bite. Melee Weapon Attack: +17 to hit, reach 15 ft., one target. Hit: 42 (6d10 + 9) necrotic damage.

Claw. Melee Weapon Attack: +17 to hit, reach 10 ft., one target. Hit: 23 (4d6 + 9) necrotic damage.

Tail. Melee Weapon Attack: +17 to hit, reach 20 ft., one target. Hit: 22 (3d8 + 9) necrotic damage.

Horrifying Visage. Each non-undead creature within 120 feet of the Vestige of the Dragon that can see it must succeed on a DC 23 Wisdom saving throw or be frightened for 1 minute. If the save fails by 5 or more, the target also ages 1d6 × 10 years. A frightened target can repeat the saving throw at the end of each of its turns, ending the frightened condition on itself on a success. If a target's saving throw is successful or the effect ends for it, the target is immune to this Vestige of the Dragon's Horrifying Visage for the next 24 hours. The ageing effect can be reversed with a greater restoration spell, but only within 24 hours of it occurring.

Necrotic Breath (Recharge 4–6). The Vestige of the Dragon exhales necrotic energy in a 90-foot cone. Each creature in that area must make a DC 24 Constitution saving throw, taking 98 (28d6) necrotic damage on a failed save, or half as much damage on a successful one.

Possession (Recharge 6). One creature that the Vestige of the Dragon can see within 15 feet of it must succeed on a DC 23 Charisma saving throw or be possessed by the Vestige of the Dragon; the Vestige of the Dragon then disappears, and the target is incapacitated and loses control of its body. The Vestige of the Dragon now controls the body but doesn't deprive the target of awareness. The Vestige of the Dragon can't be targeted by any attack, spell, or other effect, except ones that turn undead, and it retains its alignment, Intelligence, Wisdom, Charisma, and immunity to being charmed and frightened. It otherwise uses the possessed target's statistics, but doesn't gain access to the target's knowledge, class features, or proficiencies.

The possession lasts until the body drops to 0 hit points, the Vestige of the Dragon ends it as a bonus action, or the Vestige of the Dragon is turned or forced out by an effect like the dispel evil and good spell. When the possession ends, the Vestige of the Dragon reappears in an unoccupied space within 5 feet of the body. The target is immune to the Vestige of the Dragon's Possession for 24 hours after succeeding on the saving throw or after the possession ends.

The Vestige of the Dragon can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature's turn. The Vestige of the Dragon regains spent legendary actions at the start of its turn.

Detect. The Vestige of the Dragon makes a Wisdom (Perception) check.

Tail Attack. The Vestige of the Dragon makes a tail attack.

Possession (Costs 2 Actions). The Vestige of the Dragon can attempt to use its Possession ability, even if it has not recharged after a prior use.